The retina is a well-organized structure made up of repeated local circuits, which are the building blocks of retinal function. The purpose of this research program is to identify local circuits in the mammalian retina by confocal analysis of neuronal contacts, receptor localization and gap junction contacts. This will build on previous work in which the investigator has developed methods to selectively label many of the interneurons in the rod and cone pathways of the mammalian retina. Specific aim 1: Retinal Gap Junctions. Preliminary results indicate that connexin 36 is expressed in rabbit retina and that AII amacrine cells are stained with an antibody against connexin 36. The investigator will determine if Cx 36 is located at AII/AII and AII/cone bipolar cell gap junctions in rabbit and primate retina. Electron microscopy will be used to see if Cx 36 is located on both sides of AII/bipolar gap junctions. The investigator will also attempt to identify and locate other retinal connexins. This will test the hypothesis that multiple connexins are expressed by different coupled cell types in the mammalian retina. Specific aim 2: S1 and S2 amacrine cells. By confocal analysis of triple-labeled material, the investigator will test the hypothesis that S1 and S2 contacts with rod bipolar cell terminals are both apposed by GABA C receptors. A model will be developed to test the hypothesis that the size of the AII antagonistic surround depends on the distribution and synaptic contacts of S1 and S2 amacrine cells with rod bipolar terminals. Specific aim 3: Rod bipolar input to AII, S1 and S2. The investigator has developed methods by which all 3 cell types and rod bipolar terminals can be identified unequivocally with fluorescent markers. The investigator will test the hypothesis that these three post-synaptic cells have different glutamate receptors. The selective distribution of glutamate receptors may form the basis for differential processing of retinal signals. Specific aim 4: mGluR6 receptors. The investigator has raised mGluR6 antibodies in two hosts specifically to facilitate double and triple label analysis with the confocal microscope. Using these antibodies, the investigator will test the hypothesis that calbindin cone bipolar cells express mGluR6 receptors and are therefore ON bipolar cells. In addition, cone pedicles will be reconstructed to examine the distribution of the glutamate transporter GLT-1. This will test the hypothesis that GLT-1 is strategically placed to terminate the action of synaptically released glutamate. Specific aim 5: Dye-coupled amacrine cells. A new method has been developed to target coupled cells using a fluorescent dye that passes through gap junctions. ON a ganglion cells will be filled with the cationic dye POPRO 1 which will, in turn, provide a fluorescent signal to target dye-coupled amacrine cells. The investigator will test the hypothesis that different ganglion cells are dye coupled to different monostratified wide-field amacrine cell types. This may partly explain the number and diversity of amacrine cell types.